Activation of Endothelial Cells by Cocaine.

Cocaine use is associated with cardiac ischemia, sudden death, and stroke in patients with few additional risk factors for cardiovascular disease. Despite the very short halflife of cocaine in circulation (less than 1 hr), the risk of these cardiovascular events remains elevated for up to one week after cocaine ingestion. Pathologic findings following cocaine-associated cardiac events include platelet-rich microthrombi and accelerated atherosclerosis. In addition, observational studies have identified increased levels of von Willebrand Factor (VWF) at steady state in plasma of chronic cocaine abusers, which increase following cocaine challenge. Plasma VWF is derived primarily from endothelial cells, with a smaller contribution from platelets. Thus, cocaine may activate platelets and/or endothelial cells contributing to tissue ischemia, in addition to its well-known effects of vasoconstriction and increased tissue metabolic demand. When first released, VWF is hyperadhesive and capable of spontaneously binding platelets. This form, termed ultralarge VWF (ULVWF) because some of the multimers are extremely large, is normally rapidly processed by the metalloprotease ADAMTS13 into the smaller, less reactive forms usually found in plasma. Failure of this process, due to congenital or acquired deficiency of ADAMTS13, leads to accumulation of ULVWF, and in its most severe form produces the devastating microthrombotic disease, thrombotic thrombocytopenic purpura (TTP). We hypothesized that cocaine could activate the endothelium to secrete ULVWF, and thus promote thrombosis and/or vaso-occlusion. To test this possibility, we exposed cultured human umbilical vein endothelial cells (HUVEC) to various concentrations of cocaine. We found that 0.5 mg/ml cocaine, a concentration comparable to peak blood levels detectable in cocaine abusers, induced secretion of ULVWF almost as efficiently as did 25 μM histamine, a potent ULVWF secretogogue. If platelets were then perfused over the endothelium in a parallel plate flow chamber at 2.5 dyne/cm², they spontaneously formed beads-on-a-string structures on the attached ULVWF strands. We also evaluated the ability of cocaine metabolites to induce ULVWF release. Neither norcocaine nor ecoginine methyl ester (both minor metabolites) stimulated ULVWF release. However, benzoylecgonine, the major cocaine metabolite (detectable in plasma up to 6–8 days after cocaine use) potently induced ULVWF release, as detected by the formation of ULVWF strings and accumulation of higher molecular weight VWF multimers in the HUVEC supernatant on non-reducing agarose gels. These effects of cocaine are likely to contribute to cardiovascular syndromes associated with cocaine use, including the triggering of vasoocclusive crises in sickle cell anemia, and may explain the observed association of cocaine use with TTP. Furthermore, these results suggest that clinical management of cocaineinduced ischemia or vaso-occlusion may benefit from therapies aimed at disrupting ULVWF.